The invention relates to a composite fluid dynamic bearing and its manufacturing method for small motors, and particularly a composite fluid dynamic bearing and its manufacturing method capable of achieving increased production yield and improved precision.
Bearings are widely used in rotational machines to achieve the functions of support, reducing friction and carrying loads, such as in spindle motors. With continuous advances in technology, components are becoming smaller and higher precision. Demand for precision bearings is also increasing. In general, the precision bearings that are most commonly used are ball bearings. However, they also have their share of problems, such as noise, not enough rotational precision and high cost for miniaturization. Hence they cannot fully meet the requirements of miniaturization and precision. As a result, fluid dynamic bearings have been developed to provide greater precision, less noise and greater resistance to vibration.
The fluid dynamic bearing has small grooves formed on the surface of the inner hole of the bearing to contain the lubrication medium (as the grooves are very small in size, the amount of lubrication medium also is small). When the spindle rotates, the lubrication medium in the grooves is moved to generate dynamic pressure to keep the spindle in the center. As the pressure is generated by rotation, at the initial rotation stage of the spindle, the pressure is not yet generated, so that the bearing wear is occurred. In addition, machining on the inner hole of the bearing is quite difficult, and high precision dimensions are difficult to control (in general, the width of the grooves is about 100 xcexcm, while the depth of the grooves is even smaller). Oil seal and injection also are problematic.
Many techniques have been proposed in the prior art to resolve the problems with the fluid dynamic bearings mentioned above. For machining the small grooves on the surface of the inner hole of the bearing, there are techniques such as machining with cutting tools, machined by rolling, by plastics injection, by etching, by assembly, by machining after plating. However, all these methods do not completely overcome the difficulty of machining the small grooves on the inner hole surface, and the variability of forming different types of grooves. For instance, for the widely adopted xe2x80x9cherringbonexe2x80x9d groove, machining is difficult, cutting tools are difficult to make, and high precision fabrication machines are required. Some even require special cutting tools and machinery. As a result, production cost increases significantly.
The primary object of the invention is to provide a composite fluid dynamic bearing and its manufacturing method to overcome the aforesaid problems and to improve the machining of the small grooves on the surface of the inner hole and offer groove variations to increase the efficiency of the fluid dynamic bearing.
The composite fluid dynamic bearing and its manufacturing method of the invention involves dividing a bearing into a number of small sections for machining separately. The grooves formed on the surface of the inner hole of each section have a uniform slope. The sections with different groove slopes are coupled and assembled alternately to form a bearing module with pressure-generating grooves. As each section of the bearing is formed by machining with one uniform slope, precision requirements for the cutters and machinery are less severe, and precision of the grooves on the surface of the inner hole of the fluid dynamic bearing can be enhanced.
The composite fluid dynamic bearing of the invention includes a plurality of bearing sections that have grooves formed on the inner holes with different slopes. The grooves formed on the surface of the inner hole of each bearing section have a uniform slope. Each bearing section may be made by cutting the bearing that has the grooves of a uniform slope formed on the surface of the inner hole by machining. It also may be formed by directly machining on a bearing section of a selected length. Next, the bearing sections with grooves of different slopes are coupled alternately to form a bearing module with pressure-generating grooves. Then the bearing module is installed in a bearing seat to form the composite fluid dynamic bearing.
As the pressure-generating grooves of the fluid dynamic bearing are formed by machining on the bearing section, the forms of pressure-generating grooves are versatile by altering the coupling of the bearing sections. Moreover, forming the grooves of a uniform slope in the surface of the inner hole of the bearing section makes precision requirements of the cutting tools and machinery less critical. As a result, precision and efficiency of fabricating the pressure-generating grooves on the fluid dynamic bearing is improved.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.